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Lexikon


semaphore


The classic method for restricting access to shared resources (e.g. storage) in a href="module.php?name=Lexikon&file=search&eid=1&query=multi-processing">multi-processing environment. They were invented by href="module.php?name=Lexikon&file=search&eid=1&query=Dijkstra">Dijkstra and first used in href="module.php?name=Lexikon&file=search&eid=1&query=T.H.E">T.H.E href="module.php?name=Lexikon&file=search&eid=1&query=operating system">operating system. A semaphore is a href="module.php?name=Lexikon&file=search&eid=1&query=protected variable">protected variable (or {abstract data type}) which can only be accessed using the following operations: P(s) Semaphore s { while (s == 0) /* wait until s>0 */ s = s-1 } V(s) Semaphore s { s = s+1 } Init(s, v) Semaphore s Int v { s = v } P and V stand for Dutch "Proberen", to test, and "Verhogen", to increment. The value of a semaphore is the number of units of the resource which are free (if there is only one resource a "binary semaphore" with values 0 or 1 is used). The P operation href="module.php?name=Lexikon&file=search&eid=1&query=busy-wait">busy-waits (or maybe href="module.php?name=Lexikon&file=search&eid=1&query=sleep">sleeps) until a resource is available whereupon it immediately claims one. V is the inverse, it simply makes a resource available again after the process has finished using it. Init is only used to initialise the semaphore before any requests are made. The P and V operations must be href="module.php?name=Lexikon&file=search&eid=1&query=indivisible">indivisible, i.e. no other process can access the semaphore during the their execution. To avoid href="module.php?name=Lexikon&file=search&eid=1&query=busy-wait">busy-waiting, a semaphore may have an associated href="module.php?name=Lexikon&file=search&eid=1&query=queue">queue of processes (usually a href="module.php?name=Lexikon&file=search&eid=1&query=FIFO">FIFO). If a process does a P on a semaphore which is zero the process is added to the semaphore' s queue. When another process increments the semaphore by doing a V and there are tasks on the queue, one is taken off and resumed. (1995-02-01)

In addition suitable contents:
[ href="module.php?name=Lexikon&op=content&tid=31">2 ] [ href="module.php?name=Lexikon&op=content&tid=134">= ] [ href="module.php?name=Lexikon&op=content&tid=176">abstract data type ] [ href="module.php?name=Lexikon&op=content&tid=262">ad ] [ href="module.php?name=Lexikon&op=content&tid=383">af ] [ href="module.php?name=Lexikon&op=content&tid=396">ag ] [ href="module.php?name=Lexikon&op=content&tid=411">ai ] [ href="module.php?name=Lexikon&op=content&tid=433">al ] [ href="module.php?name=Lexikon&op=content&tid=544">am ] [ href="module.php?name=Lexikon&op=content&tid=592">an ] [ href="module.php?name=Lexikon&op=content&tid=740">ar ] [ href="module.php?name=Lexikon&op=content&tid=743">arc ] [ href="module.php?name=Lexikon&op=content&tid=800">as ] [ href="module.php?name=Lexikon&op=content&tid=894">at ] [ href="module.php?name=Lexikon&op=content&tid=996">av ] [ href="module.php?name=Lexikon&op=content&tid=1026">b ] [ href="module.php?name=Lexikon&op=content&tid=1181">be ] [ href="module.php?name=Lexikon&op=content&tid=1269">bi ] [ href="module.php?name=Lexikon&op=content&tid=1298">binary ] [ href="module.php?name=Lexikon&op=content&tid=1606">bs ] [ href="module.php?name=Lexikon&op=content&tid=1672">bus ] [ href="module.php?name=Lexikon&op=content&tid=1686">busy-wait ] [ href="module.php?name=Lexikon&op=content&tid=1695">by ] [ href="module.php?name=Lexikon&op=content&tid=1724">ca ] [ href="module.php?name=Lexikon&op=content&tid=1896">cc ] [ href="module.php?name=Lexikon&op=content&tid=2001">ch ] [ href="module.php?name=Lexikon&op=content&tid=2099">ci ] [ href="module.php?name=Lexikon&op=content&tid=2138">cl ] [ href="module.php?name=Lexikon&op=content&tid=2145">class ] [ href="module.php?name=Lexikon&op=content&tid=2147">classic ] [ href="module.php?name=Lexikon&op=content&tid=2791">cr ] [ href="module.php?name=Lexikon&op=content&tid=2900">cu ] [ href="module.php?name=Lexikon&op=content&tid=2976">D ] [ href="module.php?name=Lexikon&op=content&tid=3006">data ] [ href="module.php?name=Lexikon&op=content&tid=3091">data type ] [ href="module.php?name=Lexikon&op=content&tid=3136">dd ] [ href="module.php?name=Lexikon&op=content&tid=3151">de ] [ href="module.php?name=Lexikon&op=content&tid=3565">do ] [ href="module.php?name=Lexikon&op=content&tid=3752">du ] [ href="module.php?name=Lexikon&op=content&tid=3834">E ] [ href="module.php?name=Lexikon&op=content&tid=3865">ec ] [ href="module.php?name=Lexikon&op=content&tid=3896">ed ] [ href="module.php?name=Lexikon&op=content&tid=3929">ee ] [ href="module.php?name=Lexikon&op=content&tid=4111">environment ] [ href="module.php?name=Lexikon&op=content&tid=4148">er ] [ href="module.php?name=Lexikon&op=content&tid=4150">era ] [ href="module.php?name=Lexikon&op=content&tid=4171">es ] [ href="module.php?name=Lexikon&op=content&tid=4199">et ] [ href="module.php?name=Lexikon&op=content&tid=4279">exec ] [ href="module.php?name=Lexikon&op=content&tid=4286">execution ] [ href="module.php?name=Lexikon&op=content&tid=4497">fi ] [ href="module.php?name=Lexikon&op=content&tid=4514">FIFO ] [ href="module.php?name=Lexikon&op=content&tid=4520">file ] [ href="module.php?name=Lexikon&op=content&tid=4700">fo ] [ href="module.php?name=Lexikon&op=content&tid=4727">for ] [ href="module.php?name=Lexikon&op=content&tid=4828">fr ] [ href="module.php?name=Lexikon&op=content&tid=4859">free ] [ href="module.php?name=Lexikon&op=content&tid=4989">ga ] [ href="module.php?name=Lexikon&op=content&tid=5057">ge ] [ href="module.php?name=Lexikon&op=content&tid=5070">gen ] [ href="module.php?name=Lexikon&op=content&tid=5291">gr ] [ href="module.php?name=Lexikon&op=content&tid=5434">h ] [ href="module.php?name=Lexikon&op=content&tid=5686">hog ] [ href="module.php?name=Lexikon&op=content&tid=5768">hr ] [ href="module.php?name=Lexikon&op=content&tid=5931">id ] [ href="module.php?name=Lexikon&op=content&tid=6013">il ] [ href="module.php?name=Lexikon&op=content&tid=6064">in ] [ href="module.php?name=Lexikon&op=content&tid=6068">inc ] [ href="module.php?name=Lexikon&op=content&tid=6145">initialise ] [ href="module.php?name=Lexikon&op=content&tid=6407">inverse ] [ href="module.php?name=Lexikon&op=content&tid=6413">io ] [ href="module.php?name=Lexikon&op=content&tid=6449">ir ] [ href="module.php?name=Lexikon&op=content&tid=6468">iron ] [ href="module.php?name=Lexikon&op=content&tid=6482">is ] [ href="module.php?name=Lexikon&op=content&tid=6558">it ] [ href="module.php?name=Lexikon&op=content&tid=6789">ke ] [ href="module.php?name=Lexikon&op=content&tid=6792">ken ] [ href="module.php?name=Lexikon&op=content&tid=6918">la ] [ href="module.php?name=Lexikon&op=content&tid=7091">Lex ] [ href="module.php?name=Lexikon&op=content&tid=7107">li ] [ href="module.php?name=Lexikon&op=content&tid=7410">lt ] [ href="module.php?name=Lexikon&op=content&tid=7415">lu ] [ href="module.php?name=Lexikon&op=content&tid=7441">ly ] [ href="module.php?name=Lexikon&op=content&tid=7463">ma ] [ href="module.php?name=Lexikon&op=content&tid=7607">map ] [ href="module.php?name=Lexikon&op=content&tid=7817">method ] [ href="module.php?name=Lexikon&op=content&tid=8019">mm ] [ href="module.php?name=Lexikon&op=content&tid=8032">mo ] [ href="module.php?name=Lexikon&op=content&tid=8040">mod ] [ href="module.php?name=Lexikon&op=content&tid=8079">module ] [ href="module.php?name=Lexikon&op=content&tid=8167">mp ] [ href="module.php?name=Lexikon&op=content&tid=8228">ms ] [ href="module.php?name=Lexikon&op=content&tid=8258">mu ] [ href="module.php?name=Lexikon&op=content&tid=8386">na ] [ href="module.php?name=Lexikon&op=content&tid=8460">nc ] [ href="module.php?name=Lexikon&op=content&tid=8472">ne ] [ href="module.php?name=Lexikon&op=content&tid=8627">ng ] [ href="module.php?name=Lexikon&op=content&tid=8630">ni ] [ href="module.php?name=Lexikon&op=content&tid=8660">nl ] [ href="module.php?name=Lexikon&op=content&tid=8675">no ] [ href="module.php?name=Lexikon&op=content&tid=8760">ns ] [ href="module.php?name=Lexikon&op=content&tid=8787">nu ] [ href="module.php?name=Lexikon&op=content&tid=8820">O ] [ href="module.php?name=Lexikon&op=content&tid=9014">op ] [ href="module.php?name=Lexikon&op=content&tid=9061">operating system ] [ href="module.php?name=Lexikon&op=content&tid=9457">pe ] [ href="module.php?name=Lexikon&op=content&tid=9550">ph ] [ href="module.php?name=Lexikon&op=content&tid=9651">pl ] [ href="module.php?name=Lexikon&op=content&tid=9738">ply ] [ href="module.php?name=Lexikon&op=content&tid=9908">pr ] [ href="module.php?name=Lexikon&op=content&tid=9989">Probe ] [ href="module.php?name=Lexikon&op=content&tid=9995">process ] [ href="module.php?name=Lexikon&op=content&tid=10000">processing ] [ href="module.php?name=Lexikon&op=content&tid=10023">program ] [ href="module.php?name=Lexikon&op=content&tid=10042">programming ] [ href="module.php?name=Lexikon&op=content&tid=10253">query ] [ href="module.php?name=Lexikon&op=content&tid=10256">ques ] [ href="module.php?name=Lexikon&op=content&tid=10259">queue ] [ href="module.php?name=Lexikon&op=content&tid=10364">rc ] [ href="module.php?name=Lexikon&op=content&tid=10385">re ] [ href="module.php?name=Lexikon&op=content&tid=10767">ro ] [ href="module.php?name=Lexikon&op=content&tid=10918">S ] [ href="module.php?name=Lexikon&op=content&tid=11150">se ] [ href="module.php?name=Lexikon&op=content&tid=11314">sh ] [ href="module.php?name=Lexikon&op=content&tid=11324">shar ] [ href="module.php?name=Lexikon&op=content&tid=11376">si ] [ href="module.php?name=Lexikon&op=content&tid=11510">sk ] [ href="module.php?name=Lexikon&op=content&tid=11525">sl ] [ href="module.php?name=Lexikon&op=content&tid=11537">sleep ] [ href="module.php?name=Lexikon&op=content&tid=11651">so ] [ href="module.php?name=Lexikon&op=content&tid=11745">source ] [ href="module.php?name=Lexikon&op=content&tid=11934">st ] [ href="module.php?name=Lexikon&op=content&tid=12065">storage ] [ href="module.php?name=Lexikon&op=content&tid=12090">strict ] [ href="module.php?name=Lexikon&op=content&tid=12133">su ] [ href="module.php?name=Lexikon&op=content&tid=12165">sum ] [ href="module.php?name=Lexikon&op=content&tid=12246">sy ] [ href="module.php?name=Lexikon&op=content&tid=12312">system ] [ href="module.php?name=Lexikon&op=content&tid=12359">T ] [ href="module.php?name=Lexikon&op=content&tid=12360"> ] [ href="module.php?name=Lexikon&op=content&tid=12440">tc ] [ href="module.php?name=Lexikon&op=content&tid=12557">test ] [ href="module.php?name=Lexikon&op=content&tid=12588">th ] [ href="module.php?name=Lexikon&op=content&tid=12591">T.H.E ] [ href="module.php?name=Lexikon&op=content&tid=12721">to ] [ href="module.php?name=Lexikon&op=content&tid=12787">tr ] [ href="module.php?name=Lexikon&op=content&tid=12970">type ] [ href="module.php?name=Lexikon&op=content&tid=12986">ua ] [ href="module.php?name=Lexikon&op=content&tid=13030">um ] [ href="module.php?name=Lexikon&op=content&tid=13146">up ] [ href="module.php?name=Lexikon&op=content&tid=13175">us ] [ href="module.php?name=Lexikon&op=content&tid=13229">V ] [ href="module.php?name=Lexikon&op=content&tid=13252">va ] [ href="module.php?name=Lexikon&op=content&tid=13260">value ] [ href="module.php?name=Lexikon&op=content&tid=13274">var ] [ href="module.php?name=Lexikon&op=content&tid=13275">variable ] [ href="module.php?name=Lexikon&op=content&tid=13310">ve ] [ href="module.php?name=Lexikon&op=content&tid=13366">vi ] [ href="module.php?name=Lexikon&op=content&tid=13694">while ] [ href="module.php?name=Lexikon&op=content&tid=13725">win ] [ href="module.php?name=Lexikon&op=content&tid=14102">zero ]






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